1. Field of the Invention
The present invention relates to an apparatus and method for bonding a semiconductor chip on a substrate, and more particularly, to an apparatus for heating a semiconductor chip using a laser beam, a flip chip bonder having the apparatus, and a method for bonding a flip chip using the same.
2. Description of the Related Art
In recent times, electronic devices have become smaller in size but also have increased functionality, and accordingly tend to include a highly integrated and high performance semiconductor chip.
Likewise, to follow this trend, a semiconductor package that protects such a semiconductor chip from various exterior environmental factors, e.g., dust or moisture, electrical or mechanical load, etc., is manufactured to be lightweight, thin, simple and small and to have many pins.
Accordingly, a semiconductor packaging method such as a conventional wire bonding method is inadequate for newer semiconductor packages, and so new methods have been proposed. As one example of the new methods, there is a solder bump method.
In the solder bump method, a solder bump is separately formed on a pad used as input/output terminals of the semiconductor chip, and then the semiconductor chip is directly attached to a pattern of a carrier substrate or a circuit tape as it is flipped. Here, bonding is performed in the state that the semiconductor is flipped, and so this solder bump method is called “flip chip bonding.”
The flip chip bonding methods are classified into a thermal compression method and a laser compression method.
In the case of the thermal compression method, the chip is moved to a bonding position so that the solder bumps are opposed to appointed solder bumps of the carrier substrate, and then a bonding material between the solder bumps of the chip and the solder bumps of the substrate is heated to a melting point for bonding both solder bumps, which is disclosed in Japanese Patent Publication No. 2002-141376.
However, the thermal compression method has to heat the semiconductor chip for a relatively long time because heat loss arises in a heat transfer part. As a result, it takes much time to reach a bonding temperature for the solder bump, and so productivity is reduced and it is impossible to use a material vulnerable to high temperature.
Further, in the thermal compression method, the bonding position may deviate slightly due to the difference in thermal expansion coefficients between the semiconductor chip and the carrier substrate, resulting in a reduction in bonding precision. Also, the semiconductor chip and the carrier substrate contract after cooling, introducing the risk of a crack or similar damage in the bonded part.
On the other hand, the laser compression method heats and compresses the back of the chip after the chip is moved to a bonding position so that the chip solder bumps are opposed to corresponding carrier substrate solder bumps, thereby bonding both solder bumps, which is disclosed in Korean Patent Publication No. 2001-0108103. The laser compression method has been widely used because it employs a laser as a heat source for heating the semiconductor chip, and achieves high productivity and relatively low thermal expansion in a relatively short time.
FIG. 1 is a cross-sectional view illustrating an example of a bonding head in a conventional flip chip bonder.
Referring to FIG. 1, the conventional flip chip bonder includes a bonding head 10 internally formed with a vacuum passage 12. The vacuum passage 12 has vacuum pressure by a vacuum pressure generator (not shown). Thus, the bonding head 10 picks up a semiconductor chip 80 by the vacuum pressure generated in the vacuum passage 12, and carries it to a bonding position.
Further, an optical fiber 11 is provided inside the vacuum passage 12 and transfers a laser beam to the semiconductor chip 80. The optical fiber 11 transfers the laser beam from a laser generator to the semiconductor chip 80, thereby heating the semiconductor chip 80 to a bonding temperature in a relatively short time.
Thus, the conventional flip chip bonder employs the vacuum pressure generated in the vacuum passage 12 to pick up the semiconductor chip 80 and carry it to the bonding position, and uses the laser beam transferred through the optical fiber 11 to heat the semiconductor chip 80 to the bonding temperature, thereby bonding the semiconductor chip 80 to a substrate.
However, in the conventional flip chip bonder, the laser beam for heating the semiconductor chip 80 to the bonding temperature is transferred through the optical fiber 11 without a separate medium and is directly emitted to the semiconductor chip 80, and so the laser beam is not uniformly emitted to the whole region of the semiconductor chip 80. As shown in FIG. 2, the laser beam is emitted with stronger intensity at the center region of the semiconductor chip 80 than at the surrounding region and periphery of the chip 80. As a result, energy distribution in the semiconductor chip is very uneven due to the laser beam, which may cause the semiconductor chip 80 to be damaged, bonding quality to be deteriorated, or similar problems.
In other words, as the laser beam 11 is directly emitted to the semiconductor chip 80 through the optical fiber 11 without a separate medium, the intensity of the laser beam emitted to the semiconductor chip 80 has a Gaussian profile, as shown in FIG. 2. With regard to energy being proportional to the beam intensity, a center region has high energy, but its surrounding region has low energy. Therefore, in the flip chip bonding, if the intensity and the amount of the laser beam are reduced with respect to the energy in the center region, there is an energy shortage in the surrounding region, thereby causing deterioration in the bonding quality. On the other hand, if the intensity and the amount of the laser beam are increased with respect to the energy in the surrounding region, excessive energy is applied to the center region, thereby causing the semiconductor chip 80 to be damaged or the like.
To solve the above-mentioned problems, a flip chip bonder as shown in FIG. 3 has recently been used.
FIG. 3 is a cross-sectional view illustrating another example of a bonding head in the conventional flip chip bonder.
Referring to FIG. 3, this flip chip bonder further includes a laser optical unit 16 for distributing the laser beam in addition to the elements of the foregoing flip chip bonder. The laser optical unit 16 is disposed between a bottom of a bonding head 15 by which the semiconductor chip 80 is sucked and an optical fiber 11 through which a laser beam is transferred to the semiconductor chip 80. The laser optical unit 16 distributes the laser beam transferred through the optical fiber 11 to parts on one surface of the semiconductor chip 80 facing the optical fiber 11.
Thus, when the semiconductor chip 80 to be flip-chip bonded is carried, this flip chip bonder picks up the semiconductor chip 80 by vacuum pressure of a vacuum passage 12 and carries it to a bonding position, and heats the semiconductor chip 80 to a bonding temperature with the laser beam transferred through the optical fiber 11 and distributed through the laser optical unit 16, thereby bonding it to a substrate.
However, this flip chip bonder also results in the intensity of the laser beam to the semiconductor chip 80 having a Gaussian profile, as shown in FIG. 4. With regard to energy being proportional to the beam intensity, a center region has high energy, but its surrounding region has low energy. Therefore, in the flip chip bonding, if the intensity and the amount of the laser beam are reduced with respect to the energy in the center region, there is an energy shortage in the surrounding region, thereby causing deterioration in the bonding quality. On the other hand, if the intensity and the amount of the laser beam are increased with respect to the energy in the surrounding region, excessive energy is applied to the center region, thereby causing the semiconductor chip 80 to be damaged or the like.